Re: [PATCH 2/2 v6] of: add generic videomode description

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Steffen,

Thanks for the patch.

On Thursday 04 October 2012 19:59:20 Steffen Trumtrar wrote:
> Get videomode from devicetree in a format appropriate for the
> backend. drm_display_mode and fb_videomode are supported atm.
> Uses the display signal timings from of_display_timings
> 
> Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
> ---
>  drivers/of/Kconfig           |    5 +
>  drivers/of/Makefile          |    1 +
>  drivers/of/of_videomode.c    |  212 +++++++++++++++++++++++++++++++++++++++
>  include/linux/of_videomode.h |   41 ++++++++
>  4 files changed, 259 insertions(+)
>  create mode 100644 drivers/of/of_videomode.c
>  create mode 100644 include/linux/of_videomode.h
> 
> diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
> index 646deb0..74282e2 100644
> --- a/drivers/of/Kconfig
> +++ b/drivers/of/Kconfig
> @@ -88,4 +88,9 @@ config OF_DISPLAY_TIMINGS
>  	help
>  	  helper to parse display timings from the devicetree
> 
> +config OF_VIDEOMODE
> +	def_bool y
> +	help
> +	  helper to get videomodes from the devicetree
> +
>  endmenu # OF
> diff --git a/drivers/of/Makefile b/drivers/of/Makefile
> index c8e9603..09d556f 100644
> --- a/drivers/of/Makefile
> +++ b/drivers/of/Makefile
> @@ -12,3 +12,4 @@ obj-$(CONFIG_OF_PCI)	+= of_pci.o
>  obj-$(CONFIG_OF_PCI_IRQ)  += of_pci_irq.o
>  obj-$(CONFIG_OF_MTD)	+= of_mtd.o
>  obj-$(CONFIG_OF_DISPLAY_TIMINGS) += of_display_timings.o
> +obj-$(CONFIG_OF_VIDEOMODE) += of_videomode.o
> diff --git a/drivers/of/of_videomode.c b/drivers/of/of_videomode.c
> new file mode 100644
> index 0000000..76ac16e
> --- /dev/null
> +++ b/drivers/of/of_videomode.c
> @@ -0,0 +1,212 @@
> +/*
> + * generic videomode helper
> + *
> + * Copyright (c) 2012 Steffen Trumtrar <s.trumtrar@pengutronix.de>,
> Pengutronix
> + *
> + * This file is released under the GPLv2
> + */
> +#include <linux/of.h>
> +#include <linux/fb.h>
> +#include <linux/slab.h>
> +#include <drm/drm_mode.h>
> +#include <linux/of_display_timings.h>
> +#include <linux/of_videomode.h>
> +
> +void dump_fb_videomode(struct fb_videomode *m)
> +{
> +        pr_debug("fb_videomode = %d %d %d %d %d %d %d %d %d %d %d %d %d\n",

That's going to be pretty difficult to read :-) Would it make sense to group 
several attributes logically (for instance using %ux%u for m->xres, m->yres) ?

> +                m->refresh, m->xres, m->yres, m->pixclock, m->left_margin,
> +                m->right_margin, m->upper_margin, m->lower_margin, +      
>          m->hsync_len, m->vsync_len, m->sync, m->vmode, m->flag);
> +}

Shouldn't this (and the other non exported functions below) be static ?

> +void dump_drm_displaymode(struct drm_display_mode *m)
> +{
> +        pr_debug("drm_displaymode = %d %d %d %d %d %d %d %d %d\n",
> +                m->hdisplay, m->hsync_start, m->hsync_end, m->htotal,
> +                m->vdisplay, m->vsync_start, m->vsync_end, m->vtotal,
> +                m->clock);
> +}
> +
> +int videomode_from_timing(struct display_timings *disp, struct videomode
> *vm,
> +			int index)
> +{
> +	struct signal_timing *st = NULL;
> +
> +	if (!vm)
> +		return -EINVAL;
> +

What about making vm a mandatory argument ? It looks to me like a caller bug 
if vm is NULL.

> +	st = display_timings_get(disp, index);
> +

You can remove the blank line.

> +	if (!st) {
> +		pr_err("%s: no signal timings found\n", __func__);
> +		return -EINVAL;
> +	}
> +
> +	vm->pixelclock = signal_timing_get_value(&st->pixelclock, 0);
> +	vm->hactive = signal_timing_get_value(&st->hactive, 0);
> +	vm->hfront_porch = signal_timing_get_value(&st->hfront_porch, 0);
> +	vm->hback_porch = signal_timing_get_value(&st->hback_porch, 0);
> +	vm->hsync_len = signal_timing_get_value(&st->hsync_len, 0);
> +
> +	vm->vactive = signal_timing_get_value(&st->vactive, 0);
> +	vm->vfront_porch = signal_timing_get_value(&st->vfront_porch, 0);
> +	vm->vback_porch = signal_timing_get_value(&st->vback_porch, 0);
> +	vm->vsync_len = signal_timing_get_value(&st->vsync_len, 0);
> +
> +	vm->vah = st->vsync_pol_active_high;
> +	vm->hah = st->hsync_pol_active_high;
> +	vm->interlaced = st->interlaced;
> +	vm->doublescan = st->doublescan;
> +
> +	return 0;
> +}
> +
> +int of_get_videomode(struct device_node *np, struct videomode *vm, int
> index)

I wonder how to avoid abuse of this functions. It's a useful helper for 
drivers that need to get a video mode once only, but would result in lower 
performances if a driver calls it for every mode. Drivers must call 
of_get_display_timing_list instead in that case and case the display timings. 
I'm wondering whether we should really expose of_get_videomode.

> +{
> +	struct display_timings *disp;
> +	int ret = 0;

No need to assign ret to 0 here.

> +
> +	disp = of_get_display_timing_list(np);
> +

You can remove the blank line.

> +	if (!disp) {
> +		pr_err("%s: no timings specified\n", __func__);
> +		return -EINVAL;
> +	}
> +
> +	if (index = OF_DEFAULT_TIMING)
> +		index = disp->default_timing;
> +
> +	ret = videomode_from_timing(disp, vm, index);
> +

No need for a blank line.

> +	if (ret)
> +		return ret;
> +
> +	display_timings_release(disp);
> +
> +	if (!vm) {
> +		pr_err("%s: could not get videomode %d\n", __func__, index);
> +		return -EINVAL;
> +	}

This can't happen. If vm is NULL the videomode_from_timing call above will 
return -EINVAL, and this function will then return immediately without 
reaching this code block.

> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(of_get_videomode);
> +
> +#if defined(CONFIG_DRM)
> +int videomode_to_display_mode(struct videomode *vm, struct drm_display_mode
> *dmode)
> +{
> +	memset(dmode, 0, sizeof(*dmode));
> +
> +	dmode->hdisplay = vm->hactive;
> +	dmode->hsync_start = dmode->hdisplay + vm->hfront_porch;
> +	dmode->hsync_end = dmode->hsync_start + vm->hsync_len;
> +	dmode->htotal = dmode->hsync_end + vm->hback_porch;
> +
> +	dmode->vdisplay = vm->vactive;
> +	dmode->vsync_start = dmode->vdisplay + vm->vfront_porch;
> +	dmode->vsync_end = dmode->vsync_start + vm->vsync_len;
> +	dmode->vtotal = dmode->vsync_end + vm->vback_porch;
> +
> +	dmode->clock = vm->pixelclock / 1000;
> +
> +	if (vm->hah)
> +		dmode->flags |= DRM_MODE_FLAG_PHSYNC;
> +	else
> +		dmode->flags |= DRM_MODE_FLAG_NHSYNC;
> +	if (vm->vah)
> +		dmode->flags |= DRM_MODE_FLAG_PVSYNC;
> +	else
> +		dmode->flags |= DRM_MODE_FLAG_NVSYNC;
> +	if (vm->interlaced)
> +		dmode->flags |= DRM_MODE_FLAG_INTERLACE;
> +	if (vm->doublescan)
> +		dmode->flags |= DRM_MODE_FLAG_DBLSCAN;
> +	drm_mode_set_name(dmode);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(videomode_to_display_mode);
> +
> +int of_get_drm_display_mode(struct device_node *np, struct drm_display_mode
> *dmode,
> +			int index)

Same as above, do we really need to expose this helper function ? If so we 
should at least clearly document (using kerneldoc for instance) that drivers 
should only use it if they need to get a single mode once.

> +{
> +	struct videomode vm;
> +	int ret;
> +
> +	ret = of_get_videomode(np, &vm, index);
> +
> +	if (ret)
> +		return ret;
> +
> +	videomode_to_display_mode(&vm, dmode);
> +
> +	pr_info("%s: got %dx%d display mode from %s\n", __func__, vm.hactive,
> +		vm.vactive, np->name);
> +	dump_drm_displaymode(dmode);
> +
> +	return 0;
> +
> +}
> +EXPORT_SYMBOL_GPL(of_get_drm_display_mode);
> +#else
> +int videomode_to_display_mode(struct videomode *vm, struct drm_display_mode
> *dmode)
> +{
> +	return 0;
> +}
> +
> +int of_get_drm_display_mode(struct device_node *np, struct drm_display_mode
> *dmode,
> +			int index)
> +{
> +	return 0;
> +}

What about not defining those if CONFIG_DRM is not set ? No driver should call 
these functions in that case. If we really need those stubs they should return 
an error.

> +#endif
> +
> +int videomode_to_fb_videomode(struct videomode *vm, struct fb_videomode
> *fbmode)
> +{
> +	memset(fbmode, 0, sizeof(*fbmode));
> +
> +	fbmode->xres = vm->hactive;
> +	fbmode->left_margin = vm->hback_porch;
> +	fbmode->right_margin = vm->hfront_porch;
> +	fbmode->hsync_len = vm->hsync_len;
> +
> +	fbmode->yres = vm->vactive;
> +	fbmode->upper_margin = vm->vback_porch;
> +	fbmode->lower_margin = vm->vfront_porch;
> +	fbmode->vsync_len = vm->vsync_len;
> +
> +	fbmode->pixclock = KHZ2PICOS(vm->pixelclock) / 1000;
> +
> +	if (vm->hah)
> +		fbmode->sync |= FB_SYNC_HOR_HIGH_ACT;
> +	if (vm->vah)
> +		fbmode->sync |= FB_SYNC_VERT_HIGH_ACT;
> +	if (vm->interlaced)
> +		fbmode->vmode |= FB_VMODE_INTERLACED;
> +	if (vm->doublescan)
> +		fbmode->vmode |= FB_VMODE_DOUBLE;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(videomode_to_fb_videomode);
> +
> +int of_get_fb_videomode(struct device_node *np, struct fb_videomode *fb,
> +			int index)
> +{
> +	struct videomode vm;
> +	int ret;
> +
> +	ret = of_get_videomode(np, &vm, index);
> +	if (ret)
> +		return ret;
> +
> +	videomode_to_fb_videomode(&vm, fb);
> +
> +	pr_info("%s: got %dx%d display mode from %s\n", __func__, vm.hactive,
> +		vm.vactive, np->name);
> +	dump_fb_videomode(fb);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(of_get_drm_display_mode);
> diff --git a/include/linux/of_videomode.h b/include/linux/of_videomode.h
> new file mode 100644
> index 0000000..96efe01
> --- /dev/null
> +++ b/include/linux/of_videomode.h
> @@ -0,0 +1,41 @@
> +/*
> + * Copyright 2012 Steffen Trumtrar <s.trumtrar@pengutronix.de>
> + *
> + * generic videomode description
> + *
> + * This file is released under the GPLv2
> + */
> +
> +#ifndef __LINUX_VIDEOMODE_H
> +#define __LINUX_VIDEOMODE_H
> +
> +#include <drm/drmP.h>
> +
> +struct videomode {
> +	u32 pixelclock;
> +	u32 refreshrate;
> +
> +	u32 hactive;
> +	u32 hfront_porch;
> +	u32 hback_porch;
> +	u32 hsync_len;
> +
> +	u32 vactive;
> +	u32 vfront_porch;
> +	u32 vback_porch;
> +	u32 vsync_len;
> +
> +	bool hah;
> +	bool vah;
> +	bool interlaced;
> +	bool doublescan;
> +
> +};
> +
> +int videomode_to_display_mode(struct videomode *vm, struct drm_display_mode
> *dmode); +int videomode_to_fb_videomode(struct videomode *vm, struct
> fb_videomode *fbmode); +int of_get_videomode(struct device_node *np, struct
> videomode *vm, int index); +int of_get_drm_display_mode(struct device_node
> *np, struct drm_display_mode *dmode, +			int index);
> +int of_get_fb_videomode(struct device_node *np, struct fb_videomode *fb,
> int index); +#endif /* __LINUX_VIDEOMODE_H */
-- 
Regards,

Laurent Pinchart